Fiber optic cables and other cables such as CAT5 cable require that users do not bend them pass a certain amount, otherwise performance losses will be induced. This characteristic of a cable is referred to as the minimum bend radius. For example, the minimum bend radius for CAT5 cable is one inch and it is 50 mm for SMF-28 fiber optic cable when light waves having a wavelength of 1550 nm are passing through it. Any network or test instrument using these types of cable needs to maintain these minimum bend radii, otherwise the performance of the network or test instrument will be compromised. Maintaining bend radius control can be difficult, especially when fiber optic cable is routed within the interior of a small housing for a fiber optic test instrument. None of the previous methods for routing fiber optic cable in a test instrument have been successful for a number of reasons.
One previous method of routing fiber optic cable in a test instrument has been to wind the fiber into the bottom of one half of the housing of the test instrument and try to maintain bend radius control by hand. The cable is then taped into place. This method has several disadvantages. First, some assemblers are not knowledgeable about fiber optics and fail to understand the importance of maintaining bend radius control. Second, even knowledgeable and experienced assemblers will occasionally violate minimum bend radius because of the considerable amount of dexterity necessary to maintain bend radius control. Third, repeatedly taping the cable leads to microbends that reduce the optical power transmitted in the fiber to any bulkhead or connector. Finally, this method requires that the optical components be mounted to a circuit board. Minimum bend radius is often exceeded due to the transition from the bottom of the housing of the test instrument to the printed circuit board that is necessary during the process of connection of the fiber to the optical components. All of these problems lead to undesirable performance losses in the fiber and test instrument.
Another method that has been used to route fiber optic cable in a test instrument is to use fiber clips or routing channels. The disadvantage that these components have is that they typically only allow for one path for which the cable to follow. Given the variance in the length of cable used, this meant that optical components and splices would not be found in the desired location. This caused the assembler to bend the fiber in an effort to make the components fit into the available space. Another drawback is that these commercially available components were too tall to fit into a small housing, which limited their use.
Accordingly, there exists a need to provide bend radius control for cabling in a test instrument that allows the user to easily assemble the test instrument, locate optical components in the desired location, and minimize the space that the management of the cabling takes up in the test instrument.